Norma D4000 Astm

STMENGR322 Spring 2008
Lecture Notes for Polymers and Composites
June 2-6, 2008

POLYMERIC MATERIALS
Part of the reason for continual change and rapid growth of the polymer materials industry has to do with the polymer
chemistry (polymer comes from "poly" [many] + "mer" [parts]). Starting with the mers or monomers, chemists build up
the polymers. Simplest chemistry of ADDITION andCONDENSATION polymerization produces single polymer chains
of varying length. These polymers are relatively easy to describe. What makes the area complex is when the chemists
start combining polymers of different types in COPOLYMERS and POLYMER BLENDS. This infinite variety of
polymers really begs for some kind of standard classification scheme to organize our discussion of these materials.
POLYMERCLASSIFICATIONS
Good news - A STM D4000 has a complete and thorough standard classification system for polymers, copolymers,
blends, and composites. It is somewhat complex though; e.g. here is a polymer identification:

ASTM D4000-95A PA120G33A53380 GA140

Bad news - None of the polymer producers want to use the standard, preferring to keep their formulations "proprietary"
and stick to tradename identifications. But, to make sense of polymeric materials, you need to use the generic names as
much as possible.
Good news - there are only a few polymer families you need to be familiar with (see Budinski Figure 4.1).
Budinski categorizes the main polymer types as
•
•
•

THERMOPLASTICS (TP) which may be repeatedly softened for flow processing or recycling by heating.
These aregenerally tough, low strength and low cost materials.
THERMOSETS (TS) in which heating leads to chemical reactions (cross- linking) that is irreversible. These are
generally hard, brittle, and more thermally, chemically, and dimensionally stable than TP.
ELASTOMERS (EL) which have a specific definition:
o 1. at room temperature, stretch to more than 100% length,
o 2. hold for 5 minutes,
o 3.retracts to within 10% of original length within 5 minutes.

Budinski also makes separate categories for adhesives, coatings and fibers, but these are just different shapes and
applications of the main three groups.

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GENERIC POLYMER PROPERTIES
Atomic Bonding Review:
IONIC

METALLIC

COVALENT

NaCl

Any pure metal

diamond, graphite, Si-C, polymers.

Which has thehighest strength?
Why are plastics so weak? The interaction between the polymer chains is weak (van der Waals bonding) and the density
is low. Compare hardness from Budinski (figure 6-8).
What can we do to increase the strength of polymers? There are five features we should keep in mind when trying to
characterize polymer materials.

1. Chemistry of the monomer, or repeating group:
Since theultimate strength of the a polymer will depend on the strength of the bonds inn the backbone, the monomer
chemistry is critical.
EXAMPLE: Polyethylene (PE) versus Polyphenylene Sulfide (PPS)

PE relies on C-C bonds, while PPS relies of S- C bonds (not to mention that double C-C in the benzene ring). PPS is a
higher strength, higher use temperature material than PE.
[NOTE: the source of mostmonomers is either natural gas (acetals) or crude oil (everything else), which implies a
flammability issue.]

2. Molecular weight of the chain (the "n"):
Of course this is a statistically determined number for a given batch of polymer, but commonly is in the 106 range. It is
measured using a viscosity test (e.g. ASTM D-1238).
Since the long chains act like tangled spaghetti, the longer thechain (higher MW), the higher the strength: UHMWPE is
stronger than LLDPE.

3. Presence of side groups:
The monomer chemistry is such that we can fiddle with the properties of the polymer a lot by removing a H atom and
adding on a different side group.
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EXAMPLE: Polyethylene (PE) versus Polypropylene (PP)

PP is quite a bit stronger (about 5X) than PE because the larger methyl...